Primary equipment or primary devices of a power substation, like relays, switches, breakers and transformers are in many instances connected to a controller (a secondary device) with a microprocessor that is adapted for controlling the respective primary device. For example, the controller of a protection relay can measure a current flowing through the relay and can open the relay, if a fault is detected.
For configuring the primary device or for diagnostic reasons, data should be read out of the controller or sent to the controller. For example, the controller can be connected via a station-bus to a central system like a supervisory control and data acquisition (SCADA) system or a station computer. Data of the primary device or the controller can be transferred via the station-bus to the SCADA system or the station computer. In some cases, the data can be directly read out via a PC and an additional service interface of the controller. For reading data, a tool specific to the controller of the primary device should be started to interpret fault recorder data or to set configuration parameters.
If the controller of the primary device has a real time clock, the real time clock from time to time should be synchronized with a global clock.